Indeed he did, BUT, that's not why marijuana was made illegal in 1920 - 1930.
That's equivalent to claiming "Armstrong was propelled to the moon by a metal bolt.."
While that's not entirely false, you're letting out a lot of other key factors.

Also, Harry J. Anslinger was a liar and a racist. I quote him:
“Reefer makes darkies think they’re as good as white men.”
“Marihuana leads to pacifism and communist brainwashing”
“You smoke a joint and you’re likely to kill your brother.”